Chain Barrel in Loam. 6 5 In the propeller which we moulded in our last chapter (Fig. 35) a screw template was placed outside the mould. There are?cases, however, when a screw is to be moulded in loam, but n =P PATTERN -rf LJ STOPP/NG p/úCú \ where the course mentioned cannot, for certain reasons, be followed. Such is shewn at Fig. 73^. A Chain Barrel for a crane is formed with a helical groove to receive the chain. A is the casting required; B shews the striking out of the loam, and c the finished mould. The only portion requiring explanation is the screw </, made of hardwood. It is fixed to the bottom plate, and has the same pitch as the chain groove, though, of course, a more abrupt rise (for this reasc>n made as large as convenient). The striking board runs on the screw, being supported by a roller, and balanced by weight, as in the case of the propeller.